U.S. patent application number 12/445490 was filed with the patent office on 2010-04-08 for method for the production of alpha-deto acids and esters thereof.
Invention is credited to Torgrim Engell, Christian Glogard.
Application Number | 20100087679 12/445490 |
Document ID | / |
Family ID | 38961093 |
Filed Date | 2010-04-08 |
United States Patent
Application |
20100087679 |
Kind Code |
A1 |
Engell; Torgrim ; et
al. |
April 8, 2010 |
METHOD FOR THE PRODUCTION OF ALPHA-DETO ACIDS AND ESTERS
THEREOF
Abstract
The invention relates to a method for the production of a-keto
acids and esters thereof, in particular to a method of producing
.sup.13C.sub.1-.alpha.-keto acids and esters thereof i.e.
.alpha.-keto acids and esters thereof which are .sup.13C-enriched
at the C1-atom (carboxyl atom). More particularly, the invention
relates to a method of producing pyruvic acid and esters thereof,
in particular .sup.13 C.sub.1-pyruvic acid and esters thereof.
Inventors: |
Engell; Torgrim; (Oslo,
NO) ; Glogard; Christian; (Oslo, NO) |
Correspondence
Address: |
GE HEALTHCARE, INC.
IP DEPARTMENT 101 CARNEGIE CENTER
PRINCETON
NJ
08540-6231
US
|
Family ID: |
38961093 |
Appl. No.: |
12/445490 |
Filed: |
October 16, 2007 |
PCT Filed: |
October 16, 2007 |
PCT NO: |
PCT/NO2007/000360 |
371 Date: |
April 14, 2009 |
Current U.S.
Class: |
562/518 |
Current CPC
Class: |
C07C 51/15 20130101;
C07C 51/15 20130101; C07C 51/373 20130101; C07C 51/373 20130101;
C07C 57/04 20130101; C07C 59/19 20130101 |
Class at
Publication: |
562/518 |
International
Class: |
C07C 51/00 20060101
C07C051/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 17, 2006 |
NO |
20064703 |
May 18, 2007 |
NO |
20072536 |
Claims
1. Method for producing an .alpha.-keto acid of formula (I) or an
ester thereof ##STR00013## wherein R is a straight chain or
branched C.sub.1-C.sub.6-alkyl group or phenyl or benzyl,
optionally substituted with one or more hydroxyl or carboxyl
groups, said method comprising: a) obtaining a compound of formula
(II) ##STR00014## wherein R is defined as above and R' is the same
or different and denotes H or a straight chain or branched
C.sub.1-C.sub.3-alkyl group, by carboxylation of a compound of
formula (III) ##STR00015## wherein R and R' are as defined above
and X is Cl, Br or I; b) optionally converting the compound of
formula (II) into an ester; c) oxidising the compound of formula
(II) or the ester thereof to obtain an .alpha.-keto acid of formula
(I) or an ester thereof; and d) if a ester of the .alpha.-keto acid
of formula (I) was obtained in step c), optionally converting the
ester into a .alpha.-keto acid.
2. Method according to claim 1 wherein R' is the same and denotes H
or wherein R' is different and denotes H and methyl.
3. Method according to claim 1 wherein R is methyl, ethyl,
n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, phenyl, benzyl,
CH.sub.2--COOH, CH.sub.2--CH.sub.2--COOH,
CH.sub.2--(CH.sub.2).sub.2--COOH, CH.sub.2--(CH.sub.2).sub.3--COOH
or CHOH--(CHOH).sub.2--CH.sub.2OH.
4. Method according to claim 1 wherein carboxylation in step a) is
carried out by lithiation of the compound of formula (III) with an
organolithium reagent and subsequent reaction with CO.sub.2.
5. Method according to claim 1 wherein carboxylation in step a) is
carried out by generating a Grignard reagent from the compound of
formula (III) and magnesium and subsequent reaction of said
Grignard reagent with CO.sub.2.
6. Method according to claim 1 wherein the oxidation in step c) is
carried out by ozonolysis.
7. Method according to claim 1 for the production of pyruvic acid
or an ester thereof, said method comprising: a) obtaining a
compound of formula (II) ##STR00016## wherein R' is the same or
different and denotes H or a straight chain or branched
C.sub.1-C.sub.3-alkyl group by carboxylation of a compound of
formula (III) ##STR00017## wherein R' is defined as above and X is
selected from Cl, Br or I b) optionally converting the compound of
formula (II) into an ester; c) oxidising the compound of formula
(II) or the ester thereof to obtain pyruvic acid or the ester
thereof; and d) if an ester of pyruvic acid was obtained in step
c), optionally converting the ester into pyruvic acid.
8. Method according to claim 7 wherein carboxylation in step a) is
carried out by lithiation of the compound of formula (III) with an
organolithium reagent and subsequent reaction with CO.sub.2.
9. Method according to claim 7 wherein carboxylation in step a) is
carried out by generating a Grignard reagent from the compound of
formula (III) and magnesium and subsequent reaction of said
Grignard reagent with CO.sub.2.
10. Method according to claim 7 wherein the oxidation in step c) is
carried out by ozonolysis.
11. Method according to claim 1 wherein the .alpha.-keto acid of
formula (I) or the ester thereof produced by the method is an
.sup.13C.sub.1-.alpha.-keto acid or an ester thereof.
12. Method according to claim 7 wherein the pyruvic acid or ester
thereof produced by the method is .sup.13C.sub.1-pyruvic acid or an
ester thereof.
13. Method according to claim 10 wherein carboxylation in step a)
is carried out by lithiation of the compound of formula (III) with
an organolithium reagent and subsequent reaction with
.sup.13CO.sub.2.
14. Method according to claim 10 wherein carboxylation in step a)
is carried out by generating a Grignard reagent from the compound
of formula (III) and magnesium and subsequent reaction of said
Grignard reagent with .sup.13CO.sub.2.
Description
[0001] The invention relates to a method for the production of
.alpha.-keto acids and esters thereof, in particular to a method of
producing .sup.13C.sub.1-.alpha.-keto acids and esters thereof i.e.
.alpha.-keto acids and esters thereof which are .sup.13C-enriched
at the C1-atom (carboxyl atom). More particularly, the invention
relates to a method of producing pyruvic acid and esters thereof,
in particular .sup.13C.sub.1-pyruvic acid and esters thereof.
[0002] .alpha.-Keto acids and derivatives thereof play important
roles not only in organic synthesis but also in biologically active
natural products. Pyruvic acid and derivatives thereof, especially
the salts of pyruvic acid, i.e. pyruvates, are important
intermediates found in the pathway of carbohydrate metabolism
within the living body. In order to gain insight in this metabolic
pathway, .sup.13C-isotopically enriched pyruvate can be used to
detect metabolites generated in the living body by
.sup.13C-NMR.
[0003] Further, hyperpolarised .sup.13C-pyruvate may be used as
magnetic resonance (MR) imaging (MRI) agent for in vivo MR study of
metabolic processes in the human body. The term "hyperpolarised"
denotes an enhanced nuclear polarisation of the .sup.13C-nuclei
present in the pyruvate molecule. Upon enhancing the nuclear
polarisation of the .sup.13C-nuclei, the population difference
between excited and ground nuclear spin states of these nuclei is
significantly increased and thereby the MR signal intensity is
amplified by a factor of hundred and more. When using a
hyperpolarised .sup.13C-pyruvate, there will be essentially no
interference from background signals as the natural abundance of
.sup.13C is negligible and thus the image contrast will be
advantageously high. Hyperpolarised .sup.13C-pyruvate may for
instance be used as an MR imaging agent for in vivo tumour imaging
as described in detail in WO-A-2006/011810 and WO-A-2006/011809 and
for assessing the viability of myocardial tissue by MR imaging as
described in detail in WO-A-2006/054903. Hyperpolarised
.sup.13C-pyruvate is produced by for instance dynamic nuclear
polarisation (DNP) of either .sup.13C-pyruvic acid with subsequent
conversion to .sup.13C-pyruvate or by directly using
.sup.13C-pyruvate in the DNP process. The production of
hyperpolarised .sup.13C-pyruvate is described in detail in
WO-A-2006/011809.
[0004] In the body, pyruvate is converted (metabolised) into
different compounds: its transamination results in alanine, via
oxidative decarboxylation, pyruvate is converted into acetyl-CoA
and carbon dioxide (which is further converted to bicarbonate), the
reduction of pyruvate results in lactate and its carboxylation in
oxaloacetate.
[0005] Hyperpolarised .sup.13C.sub.1-pyruvate, i.e. pyruvate that
is isotopically enriched at the C.sub.1-atom (carboxyl atom) is of
most interest to be used as MR imaging agent since it has a long
T.sub.1 relaxation in human full blood (42 s at 37.degree. C.),
which allows to real-time monitor and detect by MR its conversion
to hyperpolarised .sup.13C-lactate, hyperpolarised
.sup.13C-bicarbonate and hyperpolarised .sup.13C-alanine.
[0006] Several methods for the production of pyruvic acid are known
in the art which can be grossly divided into methods involving the
use of microorganisms or enzymes and chemical synthesis.
[0007] An example of an enzyme based method for the production of
pyruvic acid is the enzymatic oxidation of lactic acid, as for
instance described in WO-A-95/00656. Enzymatic oxidation often
results in byproducts as hydrogen peroxide is produced during said
enzymatic oxidation. Further, an upscale of enzymatic processes to
an industrial process level is often problematic or impossible.
Examples for methods involving the use of microorganisms for the
production of pyruvic acid are for instance described in EP-A-313
850. A disadvantage of these microbiological production processes
is that it is often difficult and time consuming to separate,
isolate and purify pyruvic acid from the complex reaction mixtures,
e.g. form complex fermentation broths.
[0008] Examples of chemical synthesis for the production of pyruvic
acid are largely based on the oxidation of various starting
materials like propylene glycol (as described in EP-A-337 246),
hydroxyacetone (described in U.S. Pat. No. 4,247,716) or lactic
acid (see for instance JP-A-8183753). However, for the production
of isotopically enriched .sup.14C-- or .sup.13C-pyruvic acid, the
use of a commercially available isotopically enriched starting
material or an isotopically enriched starting material that is
obtainable by a straightforward chemical synthesis is greatly
preferred.
[0009] S. Anker, J. Biol. Chem 176, 1948, 133-1335 describes the
synthesis of 2-.sup.14C-enriched pyruvic acid which is obtained by
using to synthesizing 1-.sup.14C-potassium acetate from
.sup.14C-enriched barium carbonate, converting it to
1-.sup.14C-acetyl bromide and subsequently reaction with cuprous
cyanide to 1-.sup.14C-acetyl cyanide. The acetyl cyanide is reacted
to 2-.sup.14C-pyruvamide which is then hydrolysed to
2-.sup.14C-pyruvic acid. Using isotopically enriched cuprous
cyanide and acetyl bromide allows the synthesis of a pyruvic acid
that is isotopically enriched at the C1-atom; however, the use of
toxic cyanides limits the application of this method to low scale
synthesis of C1/C2-labelled pyruvic acid.
[0010] We have now surprisingly found a method to produce pyruvic
acid and pyruvic acid which is .sup.13C-enriched at the C1-atom in
excellent purity and high yield. Said method is generally useful to
produce .alpha.-keto acids and esters thereof, in particular
.alpha.-keto acids and esters thereof which are .sup.13C-enriched
at the C1-atom
[0011] Hence the invention provides a method for producing an
.alpha.-keto acid of formula (I) or an ester thereof
##STR00001##
wherein R is a straight chain or branched C.sub.1-C.sub.6-alkyl
group or phenyl or benzyl, optionally substituted with one or more
hydroxyl or carboxyl groups, said method comprising: [0012] a)
obtaining a compound of formula (II)
##STR00002##
[0012] wherein R is defined as above and R' is the same or
different and denotes H or straight chain or branched
C.sub.1-C.sub.3-alkyl, by carboxylation of a compound of formula
(III)
##STR00003##
wherein R and R' are as defined above and X is Cl, Br or I; [0013]
b) optionally converting the compound of formula (II) into an
ester; [0014] c) oxidising the compound of formula (II) or the
ester thereof to obtain an .alpha.-keto acid of formula (I) or an
ester thereof; and [0015] d) if a ester of the .alpha.-keto acid of
formula (I) was obtained in step c), optionally converting the
ester into a .alpha.-keto acid.
[0016] The term "carboxylation" denotes a chemical reaction in
which a carboxylic acid group is introduced into a substrate. In
the method of the invention, said substrate is a compound of
formula (III).
[0017] The .alpha.-keto acid of formula (I) may be obtained by the
method of the invention in form of the free acid or in the form of
a salt. By way of example the method of the invention may be used
to produce pyruvic acid and said pyruvic acid may be obtained in
form of the free acid or in the form of a salt, i.e. a pyruvate,
for instance a sodium pyruvate. Which form is obtained will depend
on the work-up procedure of the crude reaction product obtained in
step c) and said work-up procedures will be discussed later in the
application. Hereinafter and unless indicated otherwise the term
".alpha.-keto acid" denotes both the free .alpha.-keto acid and
salts of the .alpha.-keto acid. By way of example, the term
"pyruvic acid" thus denotes the free acid and salt of pyruvic acid,
i.e. pyruvates.
[0018] In the above-mentioned method, R' is the same or different
and denotes H or methyl, ethyl, n-propyl or isopropyl. The term
"the same or different" means that each of the two R'-groups in
formulae (II) and (III) are either different chemical entities or
that the two R'-groups in formulae (II) and (III) are identical
chemical entities. By way of example, if both R' groups in formula
(II) are methyl, R' is the same. If one R' group in formula (II) is
H and one R' group in formula (II) is methyl, R' is different.
[0019] In a preferred embodiment, R' is the same and denotes H. In
another preferred embodiment, R' is different and denotes H and
methyl. Embodiments wherein R' is methyl, ethyl, n-propyl or
isopropyl may facilitate oxidation in step c) compared to
embodiments wherein R' is H.
[0020] In a preferred embodiment of the method of the invention, R
is methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl or
tert-butyl. In a further preferred embodiment, R is phenyl or
benzyl. In a further preferred embodiment of the invention, R is
substituted with one or more hydroxyl or carboxyl groups and is
preferably CH.sub.2--COOH, CH.sub.2--CH.sub.2--COOH,
CH.sub.2--(CH.sub.2).sub.2--COOH, CH.sub.2--(CH.sub.2).sub.3--COOH
or CHOH--(CHOH).sub.2--CH.sub.2OH. In a most preferred embodiment,
R is methyl.
[0021] In a further preferred embodiment, the method of the
invention is used to produce .sup.13C.sub.1-.alpha.-keto acids or
esters thereof, i.e. .alpha.-keto acids or esters thereof which are
.sup.13C-enriched at the C1-atom (carboxyl atom). The
.sup.13C-enrichment the .alpha.-keto acids or esters thereof
produced by the method of the invention is preferably at least 75%,
more preferably at least 80% and especially preferably at least
90%, an isotopic enrichment of over 90% being most preferred.
Ideally, the enrichment is 100%.
[0022] Preferred .alpha.-keto acids or esters thereof--either or
not .sup.13C.sub.1-enriched--which can be produced according to the
method of the invention are phenylglyoxylic acid or esters thereof,
phenylpyruvic acid or esters thereof, 2-oxopropanoic acid, i.e.
pyruvic acid, or esters thereof, 2-oxobutanoic, i.e. .alpha.-keto
butyric acid or esters thereof, 2-oxopentanoic acid, i.e.
.alpha.-keto valeric acid, or esters thereof,
2-oxo-3-methylbutanoic acid, i.e. .alpha.-keto isovaleric acid or
esters thereof, 2-oxohexanoic acid, i.e. .alpha.-keto caproic acid
or esters thereof, 2-oxo-4-methylpentanoic acid, i.e. .alpha.-keto
isocaproic acid, or esters thereof, 2-oxobutanedioic acid, i.e.
.alpha.-keto succinic acid, or esters thereof, 2-oxopentanedioic
acid, i.e. .alpha.-keto glutaric acid, or esters thereof,
2-oxohexanedioic acid, i.e. .alpha.-keto adipic acid, or esters
thereof, 2-oxoheptanedioic acid, i.e. .alpha.-keto pimelic acid, or
esters thereof. Another preferred .alpha.-keto acid or esters
thereof which can be produced according to the method of the
invention is 2-oxo-3,4,5,6-tetrahydroxyhexanoic acid, i.e.
.alpha.-keto gluconic acid, or esters thereof.
[0023] In a most embodiment, the method of the invention is used to
produce pyruvic acid or esters thereof. In a more preferred
embodiment, the method of the invention is used to produce
.sup.13C.sub.1-pyruvic acid or esters thereof.
[0024] If an .alpha.-keto acid ester is produced by the method of
the invention, said ester may be any type of organic ester.
Preferred esters are methyl esters, ethyl esters, isopropyl esters,
tert-butyl esters and benzyl esters, most preferred esters are
methyl esters.
[0025] .alpha.-Keto acids or esters thereof obtained by the method
of the invention may be further transformed into derivates, e.g.
converted to .alpha.-keto amides or to salts of .alpha.-keto acids
by methods known in the art. Preferably, the method is used to
produce pyruvic acid, more preferably .sup.13C.sub.1-pyruvic acid,
and the .sup.13C.sub.1-pyruvic acid obtained is converted into a
salt, i.e. a .sup.13C.sub.1-pyruvate. This is preferably done by
using a work-up procedure in step c) of the method of the invention
by which the salt, i.e. .sup.13C.sub.1-pyruvate is obtained.
[0026] Preferred salts are those .sup.13C.sub.1-pyruvates which
comprise an inorganic cation from the group consisting of
NH.sub.4.sup.+, K.sup.+, Rb.sup.+, Cs.sup.+, Ca.sup.2+, Sr.sup.2+
and Ba.sup.2+, preferably NH.sub.4.sup.+, K.sup.+, Rb.sup.+ or
Cs.sup.+, more preferably K.sup.+, Rb.sup.+, Cs.sup.+ and most
preferably Cs.sup.+, as in detail described in the International
Patent Application No. PCT/N007/00109. Such salts are preferably
used for the production of hyperpolarised .sup.13C.sub.1-pyruvate
by the DNP method. The aforementioned salts are preferably obtained
by using a work-up procedure in step c) of the method of the
invention by which these salts are obtained.
[0027] Further preferred are .sup.13C.sub.1-pyruvates of an organic
amine or amino compound, preferably TRIS-.sup.13C.sub.1-pyruvate or
meglumine-.sup.13C.sub.1-pyruvate, as in detail described in
International Patent Application No. PCT/N006/00481. Again such
salts are preferably used for the production of hyperpolarised
.sup.13C.sub.1-pyruvate by the DNP method. The aforementioned salts
are preferably obtained by producing .sup.13C-pyruvic acid
according the method of the invention and converting said
.sup.13C-pyruvic acid to the aforementioned salts.
[0028] In step a) of the method of the invention, a compound of
formula (II)
##STR00004##
wherein [0029] R is a straight chain or branched
C.sub.1-C.sub.6-alkyl group or phenyl or benzyl, optionally
substituted with one or more hydroxyl or carboxyl groups; and
[0030] R' is the same or different and denotes H or straight chain
or branched C.sub.1-C.sub.3-alkyl is obtained by carboxylation of a
compound of formula (III)
##STR00005##
[0030] wherein R and R' are as defined above and X is Br, Cl or
I.
[0031] If compounds of formula (III) are used in step a), wherein R
contains hydroxyl or carboxyl groups, said groups are preferably
protected, e.g. by suitable protection groups known in the art. For
instance, hydroxyl groups may be protected as silyl ethers, derived
from the reaction of the free hydroxyl group with compounds like
tert-butyldimethylsilyl chloride or trimethylsilyl chloride.
Carboxyl groups may be protected as oxazolines or ortho-esters. The
former may be produced by reaction of the free carboxyl group or
the acid chloride thereof with 2-amino-2-methyl-1-propanol and
subsequent reaction with thionyl chloride. The latter may be
synthesized by reaction of the acid chloride of with
3-methyl-3-hydroxymethyloxethan and subsequent reaction with boron
trifluoro ethylether.
[0032] Compounds of formula (III) are commercially available
compounds and several methods known in the art may be used to carry
out the carboxylation of compounds of formula (III) to obtain
compounds of formula (II). In one embodiment, catalytic insertion
of CO results in compounds of formula (II). Catalytic insertion of
CO might be carried out in the following way: compounds of formula
(III), preferably compounds of formula (III) wherein X is Br or I,
are dissolved in a suitable solvent and portion wise added to a
solution of sodium hydroxide and a catalyst, e.g. nickel cyanide
and cetyltrimethylammonium bromide in a suitable solvent under
CO-atmosphere. The method is for instance described in H. Alper et
al., Tetrahedron Lett. Vol. 30, (20), 1989, 2615-2616. The crude
reaction product may or may not be purified before step b) or c) of
the method according to the invention. If the crude reaction
product is purified, said crude reaction product is preferably
distilled or crystallised. To obtain compounds of formula (II)
which are .sup.13C.sub.1-enriched--such .sup.13C.sub.1-enriched
compounds of formula (II) are needed as intermediates if the method
of the invention is used to produce .sup.13C.sub.1-enriched
.alpha.-keto acids or esters thereof--.sup.13CO.sub.3 which is a
commercially available compound, is used in the procedure as
described above.
[0033] In a more preferred embodiment, carboxylation is carried out
by lithiation of compounds of formula (III) and subsequent reaction
with CO.sub.2. Briefly, compounds of formula (III), preferably
compounds of formula (III) wherein X is Br or I, are dissolved in
an aprotic polar solvent like tetrahydrofuran (THF) and cooled to a
temperature below 0.degree. C. An organolithium reagent like for
instance t-BuLi in a suitable solvent is added and the mixture is
stirred to generate a lithio-derivative of compound of formula
(III), e.g. a compound of formula (III) wherein X is Li. The method
is described in for instance C. Wang et al., J. Org. Chem 2005, 70,
5150-5156 or D. Jeffery et al., Org. Lett 7, (8), 2005, 1581-1584.
The reaction mixture is then reacted with CO.sub.2 and release of
the carboxyl function, e.g. by extraction with suitable organic
solvents like dichloromethane or by distillation, yields the
compounds of formula (II). The crude reaction product may or may
not be purified before step b) or c) of the method according to the
invention. If the crude reaction product is purified, said crude
reaction product is preferably distilled or crystallised. To obtain
.sup.13C.sub.1-enriched compounds of formula (II), .sup.13CO.sub.2,
which is a commercially available compound, is used in the
procedure as described above. Any type of CO.sub.2 may be used in
the reaction. If the reaction is carried out on a low scale, solid
CO.sub.2 may be used. However, for large scale reactions and for
reactions wherein .sup.13CO.sub.2 is used, it is preferred to use
gaseous CO.sub.2 or supercritical CO.sub.2, since it is possible to
re-circulate non-used CO.sub.2, especially in a continuous
process.
[0034] In a most preferred embodiment, carboxylation is carried out
by a Grignard reaction. Briefly, a Grignard reagent is generated
from a compound of formula (III), preferably a compound of formula
(III) wherein X is Br, and magnesium in a suitable solvent like THF
and the Grignard reagent is then reacted with CO.sub.2. Release of
the carboxyl function as described in the preceding paragraph
yields the compounds of formula (II). A similar reaction is for
instance described in M. Matarrese et al., Applied Radiation and
Isotopes 57, 2002, 675-679. The crude reaction product may or may
not be purified before step b) or c) of the method according to the
invention. If the crude reaction product is purified, said crude
reaction product is preferably distilled or crystallised. To obtain
.sup.13C.sub.1-enriched compounds of formula (II), .sup.13CO.sub.2,
which is a commercially available compound, is used in the
procedure as described above. Any type of CO.sub.2 may be used in
the reaction. If the reaction is carried out on a low scale, solid
CO.sub.2 may be used. However, for large scale reactions and for
reactions wherein .sup.13CO.sub.2 is used, it is preferred to use
gaseous CO.sub.2 or supercritical CO.sub.2, since it is possible to
re-circulate non-used CO.sub.2, especially in a continuous
process.
[0035] In a preferred embodiment of the reaction described in the
previous paragraph, said reaction is carried out in a micro
reactor, e.g. a microchannel reaction system type micro reactor,
wherein the microchannel is coated with a thin film of the Grignard
reagent, or wherein the Grignard reagent is immobilized inside a
column packed with a suitable inert material to adsorb the Grignard
reagent. The micro reactor is preferably flushed with an inert gas
like argon or nitrogen before carbon dioxide gas is flushed
through. With this method, excess carbon dioxide may be recovered
downstream and re-used, which is of course especially important if
.sup.13CO.sub.2 is used. The carboxyl function may be released and
the compound of formula (II) may be recovered from the micro
reactor by flushing the reactor with for instance a basic aqueous
solution (with or without addition of an organic solvent).
Alternatively, the ester of a compound of formula (II) may be
obtained by flushing the reactor with an alcohol, for instance
ethanol.
[0036] In another preferred embodiment the reaction described above
is carried out in a continuous micro reactor system where a
solution of Grignard reagent is mixed with a CO.sub.2 flow inside a
continuous micro reactor system. By using monitoring techniques and
tools like for instance Process Analytical Tool (PAT) a steady
state condition can be obtained at the end of the reactor, for
instance by regulating the flow of CO.sub.2 into the reactor for
tuning the consumptions of reactants and thus ensuring the most
possible efficient use of said reactants.
[0037] In step b) of the method of the invention, the compounds of
formula (II) obtained from step a) are optionally converted into
esters. The conversion of carboxylic acids into esters, the
so-called esterification, is a method well known in the art wherein
a carboxylic acid is reacted with an alcohol in the presence of
protons. The crude reaction product may be used in step c). In a
preferred embodiment, the methyl esters of the compounds of formula
(II) are prepared by reaction of the compounds of formula (II) with
methanol.
[0038] In step c) of the method of the invention the compounds of
formula (II) or esters thereof are oxidised to obtain the
.alpha.-keto acids of formula (I) or esters thereof. Several
methods known in the art are suitable to oxidise the compounds of
formula (II) or esters thereof.
[0039] Suitably, compounds of formula (II) in the form of their
esters can be oxidised with hydrogen peroxide in the presence of
chromium catalysts. Briefly, CrO.sub.3, trimethylamine, hydrogen
peroxide and the compound of formula (II) in the form of its ester
are added in acetonitrile and heated to obtain an .alpha.-keto acid
ester of formula (I). The method is for instance described in M.
Inoue et al., Chemistry Letters 1989, 99-100.
[0040] Alternatively, compounds of formula (II) in the form of
their esters can be oxidised using molecular oxygen and a ruthenium
catalyst. Briefly, oxygen is bubbled through a mixture of
RuO.sub.2, acetone, pyromellitic acid and acetaldehyde, and a
solution of a compound of formula (II) in the form of its ester in
acetone is added. The mixture is stirred under oxygen atmosphere
and quenched with sodium carbonate to obtain an .alpha.-keto acid
of formula (I). The method is described in K. Kaneda et al, Chem.
Commun. 1990, 1467-1468.
[0041] In a preferred embodiment, compounds of formula (II) or
esters thereof are oxidised by ozonolysis. Briefly, ozonolysis is
carried out in a suitable solvent like for instance dichloromethane
or methanol at moderate to low temperatures. In a more preferred
embodiment, compounds of formula (II) are used as starting material
for the ozonolysis. Ozonolysis is described in for instance Y. Hon
et al., Tetrahedron 60 (2004), 4837-4860, in T. Chan et al., J.
Org. Chem. 60, 1995, 4228-4232 or in S. G. van Ornum et al., Chem.
Rev. 2006, 2990-3001.
[0042] The ozonolysis reaction may be carried out in a micro
reactor system/continuous micro reactor system as described for the
Grignard reaction on page 9.
[0043] If the reaction product of step c) is an ester of an
.alpha.-keto acid of formula (I), e.g. because the carboxyl group
had to be protected in the oxidation of step c), the free
.alpha.-keto acid of formula (I) can be obtained by methods well
known in the art, i.e. by acid- or base catalyzed hydrolysis.
[0044] If R in formula (I) contains hydroxyl and/or carboxyl groups
which were protected in the previous reaction steps, these
protection groups are removed after step c) or optional step d).
Briefly, hydroxyl groups protected as silyl ethers may be released
by reaction with fluoride reagents like tetrabutylammonium fluoride
or hydrogen fluoride. Carboxyl groups protected as oxazolines or
ortho-esters may be released by reaction with acids like hydrogen
chloride.
[0045] In a preferred embodiment, the invention provides a method
for producing pyruvic acid or esters thereof, said method
comprising: [0046] a) obtaining a compound of formula (II)
##STR00006##
[0046] wherein R' is the same or different and denotes H or
straight chain or branched C.sub.1-C.sub.3-alkyl by carboxylation
of a compound of formula (III)
##STR00007##
wherein R' is defined as above and X is selected from Cl, Br or I
[0047] b) optionally converting the compound of formula (II) into
an ester; [0048] c) oxidising the compound of formula (II) or the
ester thereof to obtain pyruvic acid or the ester thereof; and
[0049] d) if an ester of pyruvic acid was obtained in step c),
optionally converting the ester into pyruvic acid.
[0050] In a preferred embodiment, R' is the same and denotes H. In
another preferred embodiment, R' is different and denotes H and
methyl.
[0051] In a more preferred embodiment, the compound of formula (II)
of step a) is obtained by lithiation of the compound of formula
(III) with organolithium reagents, preferably organolithium
reagents like n-BuLi, t-BuLi or sec-BuLi/TMEDA. The lithiation
reaction is carried out in suitable solvents, e.g. aprotic polar
solvent like tetrahydrofuran (THF) at low temperatures e.g.
temperatures of -40.degree. C. and below. The product of the
lithiation reaction is then reacted with CO.sub.2 and release of
the carboxyl function, e.g. by extraction with suitable organic
solvents like dichloromethane or by distillation, yields the
compounds of formula (II). Any type of CO.sub.2 may be used in the
reaction, i.e. solid CO.sub.2, gaseous CO.sub.2 or supercritical
CO.sub.2. The crude reaction product may or may not be purified
before step b) or c) of the method according to the invention. If
the crude reaction product is purified, said crude reaction product
is preferably distilled.
[0052] The reaction is shown in reaction scheme 1:
##STR00008##
[0053] In a most preferred embodiment, the compound of formula (II)
of step a) is obtained by reaction of a compound of formula (III),
preferably a compound of formula (II) wherein X is Br with
magnesium to form the Grignard reagent. The reaction is suitably
carried out at room temperature or above in a polar aprotic solvent
like THF. The Grignard reagent is then reacted with CO.sub.2 and
release of the carboxyl function, e.g. by extraction with suitable
organic solvents like dichloromethane or by distillation, yields
the compounds of formula (II). Again any type of CO.sub.2 may be
used in the reaction. The crude reaction product may or may not be
purified before step b) or c) of the method according to the
invention. If the crude reaction product is purified, said crude
reaction product is preferably distilled.
[0054] The reaction is shown in reaction scheme 2:
##STR00009##
[0055] The conversion of the compound of formula (II) into to an
ester in step b) might or might not be carried out, depending on
the method of oxidation which is chosen for step c). In a preferred
embodiment, the oxidation method is ozonolysis and if pyruvic acid
itself is the desired reaction product, conversion of the compound
of formula (II) into an ester in step b) is preferably not carried
out.
[0056] If the method described above is used to produce an ester of
pyruvic acid, the conversion of the compound of formula (II) into
an ester is conveniently carried out in step b) by methods well
known in the art. Preferably, the methyl ester, by reaction of the
compound of formula (II) with methanol and said crude ester is used
in step c) of the method described above without any further
purification steps.
[0057] In a preferred embodiment of the method above, the compound
of formula (II) or the ester thereof, if step b) has been carried
out, is oxidised to pyruvic acid or the ester thereof by
ozonolysis, preferably by ozonolysis in dichloromethane, methanol
or a mixture thereof as a solvent at moderate to low temperatures,
i.e. room temperature to temperatures of about 0.degree. C. and
below, e.g. -78.degree. C. The completion of the reaction is
indicated by a blue colour in the reaction mixture caused by an
excess of free ozone. Said free ozone may be removed by passing a
stream of for instance nitrogen gas or oxygen gas through the
reaction mixture. An (unstable) ozonoid is formed during the course
of the reaction. If the reaction is carried out at moderate
temperatures said ozonoid will react to the desired pyruvic acid or
ester thereof. At low temperatures an oxidizing or reducing agent
is needed to convert the ozonoid to the desired reaction product.
Oxidizing agents are known in the art and examples of suitable
oxidizing agents are peroxyacids, silver oxide, chromic acid,
oxygen, permanganates or hydrogen peroxide. Reducing agents are
known in the art and examples of suitable reducing agents are zinc
acetic acid, sulfite ions, bisulfite ions, iodide, dimethylsulfide
or thiourea.
[0058] In one embodiment, the solvent is evaporated and the crude
reaction product is preferably purified, preferably by
distillation. In another embodiment, the solvent is evaporated and
the crude reaction product is purified by crystallization. This may
be done by evaporating the solvent and addition of water and a base
to convert pyruvic acid into a salt, i.e. a pyruvate. The mixture
is then left for crystallization. In a preferred embodiment, said
base in an inorganic sodium base, preferably NaOH.
[0059] Obtaining the salt rather than the free pyruvic acid is of
advantage with regard to shelf life/stability. Pyruvic acid is not
a very stable compound and by storing pyruvic acid in the form of
its salts, e.g. in the form of sodium pyruvate this problem can be
overcome. Alternatively, the pyruvate obtained by crystallization
may be converted into free pyruvic acid in a subsequent step and
method for this conversion are known in the art.
[0060] The ozonolysis reaction is shown in reaction scheme 3:
##STR00010##
[0061] If an ester of pyruvic acid was obtained in step c) said
ester may optionally be converted into pyruvic acid by methods well
known in the art, e.g. acid- or base catalyzed hydrolysis.
[0062] In a more preferred embodiment, the invention provides a
method for producing .sup.13C.sub.1-pyruvic acid or esters thereof,
said method comprising: [0063] a) obtaining a compound of formula
(II)
##STR00011##
[0063] wherein R' is the same or different and denotes H or
straight chain or branched C.sub.1-C.sub.3-alkyl by carboxylation
of a compound of formula (III)
##STR00012##
wherein R' is defined as above and X is selected from Cl, Br or I
[0064] b) optionally converting the compound of formula (II) into
an ester; [0065] c) oxidising the compound of formula (II) or the
ester thereof to obtain .sup.13C.sub.1-pyruvic acid or the ester
thereof; and [0066] d) if an ester of .sup.13C.sub.1-pyruvic acid
was obtained in step c), optionally converting the ester into
.sup.13C.sub.1-pyruvic acid.
[0067] In a preferred embodiment, R' is the same and denotes H. In
another preferred embodiment, R' is different and denotes H and
methyl.
[0068] The method of the invention for producing
.sup.13C.sub.1-pyruvic acid or esters thereof is carried out as
described for the method of the invention for producing pyruvic
acid or esters thereof, however, instead of CO.sub.2,
.sup.13CO.sub.2 is used in reaction step a). Further it is
preferred to purify the crude reaction product of step a) by
distillation and the final reaction product of step c) or d) by
distillation. In another embodiment, the final reaction product of
step c) or d) is purified by crystallization as described above by
converting pyruvic acid into a salt, i.e. a pyruvate.
[0069] In a preferred embodiment, the method of the invention is
used for producing .sup.13C.sub.1-pyruvic acid, i.e. step d) is not
carried out and the reaction product of step c) is purified by
distillation.
[0070] In another preferred embodiment, the method invention is
used for producing .sup.13C.sub.1-pyruvate, more preferably sodium
.sup.13C.sub.1-pyruvate, i.e. step d) is not carried out and the
reaction product of step c) is purified by crystallization as
described above.
[0071] FIG. 1 shows a flow chart of a preferred embodiment of the
invention for the production of pyruvic acid or
.sup.13C.sub.1-pyruvic acid in the form of the free acid or in the
form of its sodium salt.
[0072] The invention is further illustrated by way of the
Examples.
EXAMPLES
Example 1a
Synthesis of Methacrylic Acid, a Compound of Formula (II), by
Grignard Reaction Starting from 2-Bromopropene, a Compound of
Formula (III)
[0073] 2-Bromopropene (24.20 g, 200 mmol) dissolved in
tetrahydrofuran (THF, 100 ml) was added drop wise to a stirred
suspension of magnesium turnings (4.38 g, 180 mmol) in THF (100 ml)
under nitrogen-atmosphere. The 2-bromopropene was added at a rate
causing the reaction mixture to boil gently. After complete
formation of the Grignard reagent had been achieved, the mixture
was stirred at room temperature for 30 min, before being cooled to
-70.degree. C. The reaction mixture was subjected to an atmosphere
of carbon dioxide (1 bar) under heavy stirring (vortexing). The
reaction was allowed to reach room temperature and then terminated
by addition of saturated aqueous ammonium chloride (100 ml). THF
and excess 2-bromopropene was removed in vacuo at 30.degree. C. and
the aqueous phase was acidified by addition of aqueous HCl (3M, 50
ml) before extraction with dichloromethane (3.times.50 ml). The
combined organic extracts were dried over magnesium sulfate and
evaporated to give the title compound; a colourless or slightly
yellow oil. Yield: 13.50 g (87%), purity 99%.
Example 1b
Synthesis of Methacrylic Acid, a Compound of Formula (II), by
Catalytic Insertion of CO Starting from 2-Bromopropene, a Compound
of Formula (III)
[0074] To a mixture of tetrakis(triphenylphosphine)palladium (0.29
g, 0.25 mmol), hexadecyltrimethylammonium bromide (0.36 g, 1.0
mmol) and 2-bromopropene (1.16 g, 10 mmol) in toluene (20 ml) was
added aqueous NaOH (5M, 20 ml, 100 mmol). The mixture was subjected
to an atmosphere of carbon monoxide (1 bar) and heated to
95.degree. C. for 2 h. The phases were separated and the organic
phase was extracted with aqueous NaOH (1 M, 2.times.20 ml). The
aqueous phase was washed with dichloromethane (50 ml). The aqueous
phase was acidified using aqueous HCl (3 M) and extracted with
dichloromethane (3.times.50 ml). The combined organic extracts were
dried over magnesium sulfate and evaporated in vacuo at 30.degree.
C. to give the product; a colourless or slightly yellow oil. Yield:
0.52 g (60%).
Example 2
Synthesis of Pyruvic Acid, a Compound of Formula (I) by Ozonolysis
of Methacrylic Acid, a Compound of Formula (II)
[0075] A solution of methacrylic acid obtained in Example 1a or 1b
(8.61 g, 100 mmol) was dissolved in dichloromethane/methanol (1:1
v/v, 50 ml) and cooled to -78.degree. C. A stream of ozone was
passed through the solution until the solution turned blue.
Dimethylsulfide (12.41 g, 200 mmol) was added and the mixture was
allowed to reach room temperature. The reaction mixture was
evaporated in vacuo and the residue was distilled. The product was
isolated as colourless oil. Yield: 7.95 g (90%).
Example 3
Synthesis of Pyruvic Acid, a Compound of Formula (I) by Ozonolysis
of Methacrylic Acid, a Compound of Formula (II)
[0076] A solution of methacrylic acid obtained in Example 1a or 1b
(4.68 g, 54 mmol) in dichloromethane/methanol (5% methanol, 50 ml)
was cooled to -78.degree. C. and a stream of ozone was passed
through until the solution turned blue. Dimethylsulfide (12.41 g,
200 mmol) was added and the mixture was allowed to reach room
temperature. Excess dimethylsulfide was removed by passing a stream
of nitrogen through the reaction mixture. The reaction mixture was
evaporated in vacuo at 30.degree. C. and the residue was distilled.
The product was isolated as colourless oil. Yield: 4.40 g (98%).
Purity: 97%.
Example 4
Synthesis of Pyruvate, a Salt of a Compound of Formula (II) by
Ozonolysis of Methacrylic Acid, a Compound of Formula (II)
[0077] A solution of methacrylic acid obtained in Example 1a or 1b
(15.31 g, 178 mmol) in dichloromethane/methanol (5% methanol, 50
ml) was cooled to -78.degree. C. and a stream of ozone was passed
through until the solution turned blue. Dimethylsulfide (12.41 g,
200 mmol) was added and the mixture was allowed to reach room
temperature. Excess dimethylsulfide was removed by passing a stream
of nitrogen through the reaction mixture. The reaction mixture was
evaporated in vacuo at 30.degree. C. To the residue was added water
(100 ml) and then slowly added a solution of aq. NaOH (1 M, 178
ml). The mixture was concentrated and left for crystallisation at
4.degree. C. The white crystalline material obtained was filtered
and washed with acetone (3.times.100 ml). Yield: 14.50 g (92%).
Purity: 95%.
* * * * *